Holograms and diffraction gratings have become very popular in recent years for their decorative effect. In addition, because holograms and diffraction gratings, hereinafter "holograms" are hard to produce or reproduce without sophisticated equipment and personnel, they have found wide application as a means for authenticating documents and other objects ranging from credit cards to limited edition collectibles. The popularity of holograms has been enhanced by economical, high-volume methods of producing them, such as the production of reflection holograms by embossing a web substrate to form a surface microcorrugation or microtexture representing an interference fringe pattern.
The various steps involved in the creation of holographic microtextured surfaces are well known and need not be described herein except to note that a few different methods for mass production exist, e.g., embossing, as exemplified by the patents to U.S. Pat. No. 3,758,649 to Frattarola, U.S. Pat. No. 3,922,416 to Ryan, and U.S. Pat. No. 5,164,227 to Miekka et al. An alternative novel embossing method is proposed in a copending U.S. patent application Ser. No. 07/998,832 filed Dec. 30, 1992 entitled METHOD OF PRODUCING SURFACE RELIEF HOLOGRAMS and assigned to the assignee herein.
In addition to embossing processes, casting techniques have also been proposed. For example, U.S. Pat. No. 5,083,850 to Mallik et al. discloses a casting process employing liquid resin casting of microtextured surfaces through photopolymerization.
In the course of their use as decoration and security devices, holograms are frequently employed in association with other traditional indicia, such as printing, photographs and handwriting. For example, a driver's license may bear an individual's photograph, signature, registration number and address, along with other information. For verification purposes, holographic indica, e.g., the state seal, may be incorporated into a license by laminating or gluing it thereto in a manner which prevents non-destructive alteration of the various elements of the card, i.e., to prevent forgery. This has given rise to various strategies for associating a hologram, which is hard to produce or reproduce without sophisticated and expensive apparatus, with a document to be secured. It is advantageous if the hologram is non-removable from the entirety of the document to be protected. This raises a problem however, in that, if a hologram is overlain upon other indicia, the underlying indicia is obscured. Solutions to this problem have been proposed. For example, U.S. Pat. Nos. 5,044,707, 5,128,779 and 5,145,212 to Mallik describe discontinuous holograms which are partially transparent owing to a discontinuous reflective layer. Copending U.S. patent application Ser. No. 08/048,769 filed Apr. 16, 1993 entitled SEMI-TRANSPARENT LAYER FOR A PHASE HOLOGRAM and assigned to the assignee of the present application proposes yet another solution in the form of an embossed reflection hologram having a continuous, semi-transparent reflective layer. In both cases, a compromise is struck between the brightness of the hologram and the visibility of the underlying indica.
In U.S. Pat. No. 5,083,850, Mallik et al. propose a technique for coating a hardened surface relief created by a liquid casting process with a discontinuous graphical pattern of a clear or colored paint that eliminates the surface relief pattern in the regions so coated. Mallik '850 suggests that the paint can be applied in the form of printing, which is understood to mean words. Mallik '850 also recognizes that printing can be applied to a web of diffraction grating media on the side which is opposite to the casted microtexture. While Mallik '850 conceptually explores applying some form of graphical pattern to a diffraction grating, Mallik '850 fails to supply sufficient information to carry out this technique, e.g., by failing to specify the "paint" to be used and the exact means by which this "paint" is applied. In addition, Mallik '850 is applicable to techniques involving holograms cast from liquid photocurable resin.
As applied to embossed media, when an application requires printed indicia in combination with holographic indicia, a web of existing metallized holographic material is overprinted on the viewing side, opposite to the microtexture and metallization. This is typically performed by the end user who has purchased holographic material without any printing on it. Frequently, this occurs after the holographic material is applied to product packaging. It would be beneficial, therefore, if an end user could obtain a holographic web from the manufacturer which already incorporated any desired printing, as this would eliminate the relatively difficult step of printing upon packaging at the end user's location.
Accordingly, the present invention provides a specific method for applying non-holographic printed indicia to an embossed, rather than cast, reflection hologram. The process yields a mixed holographic/non-holographic media which is ready for use by an end user without any subsequent priming steps.